Apparatus for bleaching pulp



Dec. 22, 1936 MwW/fl @0211, @s i' lva mil/L15 MD affer Patented Dec. '22, 1936 -U EDQ T PATENT FI Mathew F. McCombs and Francis W. Decker,

Niagara Falls, N. ,Y., assignors to Niagara Al- I kali Company, Niagara Falls,- N. Y., a corpora-' tion of New York w r Applicationseptember 5, 1935, Serial No. 39,353

-30laims.

overlying and enclosing the inlet pipe but spaced therefromas well as from thetbp, sides and bottom of theshell, to' direct the pulp after its up- 15 ward how through the inlet pipe, downwardly tothebottom of the she'll and thence again upwardly between the shell and partition to the outlet", means-forinjectingmilk of lime or other neutralizingagent into the pulp in the outlet pipe,

,and an-agitator'ln the outlet pipe beyond such injectorto agitateand intermix the injected milk of lime withthe' pulp so emerging from the ap- 1 paratus;"all' as'more fully hereinafter set forth anda'sclaimed.

25 in producingipiilp, wood and woody fibers are. chemically digested"to' dissolve'lignin and leave cellulose. some; lignin'fis always 'left and the fibermust afterwards be, bleached. With a fargoing digestionthe resulting pulp usually has a weak fibrous'structure. {with less removal of lignin desirable fiber strength is obtainedin the pulp but it "is hard bleachingit req res treatment with atensiderebiamtunt'ot chlorin. In treat-' ing hard'bleaching pulpit is essential to prevent weakening of the fiber. Itis' a desideratum in the art to produce astrong hard bleaching pulp and then 'bleach it; without sacrifice of strength.

In bleaching-if the pulp is not uniformly exposedftofthe chlorinatingagentsome parts are apt to be excessively treated with other parts undertreated. It is hard to secure uniform fargoing bleaching 'without anysacrifice of strength. i

object accomplished in this invention is providing apparatus for bleaching pulp under 5 accurate control ofbleaching conditions, thereby producing'a pulp of uniform character and of good strength.

In securing this object e s to be bleached j is passed alternately in reverse fiow through aparatus in interm'ixturewith an injected chlorinating agent to subject all parts of the pulp massfequallygto chemical action while in continuous how, and atthe same time to permit I accurate control of bleaching conditions. Appa- 55 ratus is' provided wherein chlorin is injected into a flowing stream of pulp and mechanically intermixed, therewith by-an agitator, beforepassing into a shell which is providedwith a concentrically mounted partition for directing the flow on of pulp in a tortuous stream therethrough, means or other neutralizing agent into the so treated pulp as it emerges from the apparatus, together with mechanical agitating means beyond the in-. jector to assist the flow of pulp and aid in the thorough intermixture of milk of lime therewith.

Other and further objects will be apparent from the following description of drawing wherein the single figure is a side view, partly in vertical section, of apparatus embodying our invention. 'I

A mass of pulp which is to undergo treatment flows in a continuous stream to the apparatus through inlet pipe l into which an injector pipe I I extends for feeding a chlorinating agent there to, as forexample chlorin gas from apparatus such as is shown in our copending' application Serial No. 39,354, filed September 5, 1935, which provides for the continuous controlled -fiow1oi. chlorin to such a process. Y A mechanical agitator I! of conventional de-, sign is mounted in the pipe Ill beyondvthe injector It so that the pulp and chlorin are pre:

liminarily intermixed before entering the-apparatus now to be described.

The inlet pipe H) has a verticalleg l3 which,

extends upwardly through the outwardly dished bottom ll of a vertical shell '[5 and terminates] at a point in the upper portion of the shell. QThfe shell I5 is mounted upon supportslli and has a valved discharge outlet I! in its bottom.

An annular partition-element l8 mounted, as by spacers l9, within theshell to surroundand enclose the vertical leg l3 of the inlet 'pipefand such partition has a frusto-conical top 20 which is spaced from the similarly shaped top 2| of the shell. The bottom of the annular partition terminates above the bottom of the shell and its frusto-conical top is formed'with a small open whichmight impede the fiow of pulp. The pulp flows from the inlet to the outlet with 'a mini mum of frictional resistance'against the apparatus walls.

-Milk of lime from the storage container 26 is forced by a pump 21 through piping 2B and 29 to the injection nozzle 25. The pipe 28 has a return-30 to the storagetank 26 so that excess milk of lime not needed for'the process will return to storage. The pump 21 therefore estab-' lishes a continuous circulation from and back to the storage tank; the excess milk of lime so circulated being by-passed back to the tank while such of it as is required for the process will flow through the branch pipe 29 to the injector nozzle 25. A gage 3| is provided in the pipe 29 forindicating the flow of milk of lime to the process through orifice 32 and such flow may be regulated according to requirements by a valve 33, also in piping 29.

The milk of lime may conveniently be drawn from a supply tank 34 which contains unscreened milk of lime by means of pump 35 and piping 36 into the storage tank 26 which, further, has a lime screen 31.

In the outlet pipe 23, beyond the injection nozzle 25, there is mounted an agitator 38 similar to the agitator l2 in the inlet. This device assists in the thorough mixing of the milk of lime and pulp passing from the apparatus through the pipe 23.

While not specifically shown in the drawing, the piping, shell and partition are advantageously all rubber covered to protect the metal from chemical action. Instead, any applicable corrosion-resistant varnish may be used.

From the foregoing it will be apparent that our apparatus provides for the thorough mixing of pulp in a bleaching process whereby all parts of its mass are subjected to the action of the bleaching agent so that accurate control of bleaching conditions is assured and a pulp of uniform character will result. The outer casing and inner partitions are so arranged that no short-circuiting or channeling of the flowing mass of pulp can occur; that is, the pulp-chlorin mixture must flow through the entire length of the tortuous path provided. This insures a steady flow of uniformly treated pulp. With the partition arrangement described it is not necessary to use a mechanical agitator. This is an advantage. Provision of pumps, impellers, etc. which will operate in the presence of corrosive liquids is a difiicult problem. Ordinarily, it is most convenient to process a rather fluid pulp suspension, but the apparatus is well adapted for treatment of semi-fluid or plastic suspensions.

What we claim is:

1. Apparatus for bleaching pulp with chlorin and providing prolonged and intimate contact of chlorin and pulp, said apparatus comprising means for introducing chlorin .at a controlled rate into a flowing mass of pulp, an agitator for causing intimate mixture of the pulp with the chlorin so introduced, a container shell, an unrestricted inlet pipe extending to the upper part of the shell and through which the pulp flows upwardly into the shell, a cylindrical partition within the shell and surrounding said inlet pipe, a frusto-conical top for said partition to direct the flowing pulp downwardly in the annular space between the partition and inlet pipe, said partition terminating above the bottom of the shell to provide an unrestricted passage for the pulp therearound whereby itwill flow again upfrusto-conical top onsaid shell, an outlet pipe communicating with saidtopymeans for injecting. neutralizing agent into the mass of pulp emerging into the outlet pipe and a mechanical agitator for causing intimate mixture of the pulp and neutralizing agent and for assisting in moving the pulp through said outlet pipe. i

2.' Apparatus for bleaching pulp with chlorin and providing prolonged and intimate contact of chlorin and pulp, said apparatus comprising a container shell-having an outwardly dished bottom and a frusto-conical top, an unrestricted inlet pipe for pulp extending through said bottom and terminating in the upper portion of the inlet pipe, downwardly between said pipe and partition, and thence again upwardly between the partition and shell, to the outlet, said container shell, inlet pipe, partition and partition top being so constructed and arranged as to form an unrestricted progressively expanding passageway for the pulp, together with means for injecting. chlorin into the pulp mass before entering said shell, and means for injecting neutralizing agent into the so treated pulp mass emerging from said shell, the inlet pipe being so constructed and arranged as to maintain the shell full of pulp during operation.

3. Apparatus for bleaching pulp with chlorin and providing long and intimate contact of chicrin and pulp, said apparatus comprising a cylindrical shell having an outwardly dished bottom and a frusto-conical upper end, an unrestricted inlet pipe for pulp extending from a level above the top of the shell, downward below the shell, upwardly through said bottom and upwardly into the shell coaxial therewith, whereby the shell is maintained full of pulp during operation, an outlet plpe in communication with the shell at the top of its frusto-conical end, a cylindrical partition suspended within said shell and having a frusto-conical top, the lower end of said partition being spaced above the bottom of said shell, spacing means for suspending the said partition equidistant from the walls and top 01' said shell without imposingany substantial restriction of the space between partition and shell, the said upwardly projecting inlet pipe extending into the chamber defined by said partition and terminating in the plane of the base of the frusto-conical topthereof, said inlet pipe, partition, partition ltop, shell and shell bottom being so constructed and arranged as to provide an unrestricted progressively expanding passageway for the pulp, means for injecting measured quantities of chlorin into the mass of pulp in said inlet pipe, a mechanical agitator in said pipe for causing intermixture of chlorin with the pulp prior to its entry into the said shell and for assisting its flow therethrough upwardly through said inlet pipe, thence downwardly between said inlet pipe and annular partition, and again upwardly between said partition and the shell to the outlet pipe, together with means for injecting neutralizing agent into the pulp emerging from said shell, and an agitator in said outlet pipe therebeyond for causing intimate mixture of such neutralizing agent with the pulp and for assisting flow of pulp through the outlet pipe.

MATHEW F. McCOMBS. FRANCIS W. DECKER. 

